1. Field of the Invention
The present invention relates to a structure of a sealing apparatus for closely sealing an annular space formed between an inner member and an outer member which are relatively rotated to each other. More particularly, the present invention relates to a sealing apparatus having a rotation detecting apparatus for detecting a rotational speed of front and rear wheels in an anti lock brake system of a motor vehicle. The sealing apparatus in accordance with the present invention is employed also in a field of an electrical appliance, an industrial machine, a bicycle or the like.
2. Description of Background Art
In conventional, as shown in FIG. 3, there has been developed a sealing apparatus 105 for closely sealing an annular space between an inner member 101 and an outer member 102 which are relatively rotated to each other via a rolling element 103, in which a magnetic encoder 106 is integrally formed with the sealing apparatus 105. The sealing apparatus 105 is structured such that first and second seal annular members 107 and 108 each formed in an L-shaped cross section are respectively fitted to the inner member 101 and the outer member 102, and a seal lip 109 is provided in the second seal annular member 108, and the seal lip 109 is brought into slidable contact with the first seal annular member 107. The magnetic encoder 106 is formed by an encoder member 111 made of a rubber elastic body such as a rubber or a resin in which a magnetic material powder is mixed, and is vulcanized and bonded to an outer side in an axial direction (a rightward direction in the drawing) of the first seal annular member 107. The encoder member 111 is structured such that magnetic poles are alternately formed in a circumferential direction, and is detected by a magnetic sensor 110 which is arranged close thereto.
However, in the structure mentioned above, since the magnetic encoder 106 and the magnetic sensor 110 are arranged at a position exposed to an atmospheric air in an outermost side in an axial direction, the magnetic encoder 106 and the magnetic sensor 110 are under a severe condition directly exposed to a spattering muddy water or foreign matter. If the muddy water makes an intrusion thereinto, rust generation is caused, thereby lowering a performance of detecting the rotational speed. Further, if the foreign matter makes an intrusion thereinto so as to be attached to a portion between the magnetic encoder and the magnetic sensor, there is a risk that the magnetic encoder or the magnetic sensor are damaged due to rotational jamming of the foreign matter in the worst case so as to lead the detected rotational speed into error. As a countermeasure thereof, in Japanese Unexamined Patent Publication Nos. 11-303879 and 2002-333033, there has been proposed a structure in which a magnetic encoder is wrapped by a protection plate arranged in an outer side in an axial direction of the magnetic encoder, and the protection plate integrally formed with the magnetic encoder is assembled in an inner member. However, in this structure, the muddy water or the foreign matter making an intrusion can not be sufficiently excluded, and there is a problem that the magnetic encoder is exposed to an abnormal compression or deformation at a time when the protection plate integrally formed with the magnetic encoder is assembled, whereby a detecting accuracy is deteriorated. Further, since the protection plate and the magnetic encoder are fitted and thereafter fitted to the inner member, the fitting force is weakened. Further, since end portions of the protection plate and the first seal annular member are exposed to the rolling element side, there is a risk that a grease within a bearing portion makes an intrusion from a portion between both the rings.